Shatapatha Brahmana 14.3.1.29

14.3.1.29

atha prasute dadhigharmeṇa caranti yajño vai somaḥ śiraḥ pravargyo yajña evaitaciraḥ pratidadhāti mādhyandine savana etadvā indrasya niṣkevalyaṃ savanaṃ yanmādhyandinaṃ savanaṃ sva evainametadbhāge prīṇāti stute mādhyandine pavamāne prāṇo vai mādhyandinaḥ pavamānaḥ prāṇamevāsminnetaddadhātyagnihotrahavaṇyā mukham vā etadyajñānāṃ yadagnihotraṃ śīrṣaṃstanmukhaṃ dadhāti

And at a continued pressing of Soma they also perform the Gharma of curds and whey (Dadhi-gharma),--for Soma is the sacrifice, and the Pravargya is its head: he thus restores to the sacrifice its head,--at the midday-pressing, for that--to wit, the midday-pressing--is Indra's special pressing: he thus pleases him in his own share;--when the Mâdhyandina-pavamâna has been chanted, for the Mâdhyandina-pavamâna is the breath: it is breath he thereby lays into him;--with the Agnihotra-ladle, for the Agnihotra is the mouth of sacrifices: he thus puts a mouth in the head.